EXPERT TOPIC SALMON
SALMON
EXPERT TOPIC Lice and laserbeams
by Vaughn Entwistle, Features Editor, International Aquafeed
A
quaculture’s biggest dilemma that has recently burst onto the front pages of mainstream media: The challenges of sea lice and their effects upon both farmed and wild salmon. Sea lice (despite the insect name they are actually a small crustacean) are marine parasites that latch onto fish such as salmon and feed upon the mucus, tissue and blood of the host fish. Sea lice infestations have been implicated in the decline of wild salmon and sea trout stocks. Moreover, it is a global problem that is impacting all the major salmon farming nations: USA, Canada, Scotland, Norway and Chile. A particular species of sea louse (Lepeophtheirus salmonis) is often found on farmed and wild Atlantic salmon, while another species (Caligus rogercresseyi) has become a major concern in Chilean salmon farms. Sea lice have colonised nearly every aquatic environment on earth. They have been around for millions of years and have adapted to live on salmonids (fish of the salmon family, which includes salmon, trout, grayling and whitefish), feeding on the fishes’ skin and blood to survive. The lice have a short, freeswimming larval phase, when they need to find and attach to a fish host. The sea louse’s life cycle consists of a series of molts— at the ‘napulii’ stage the sea louse is free swimming, relying on its own internal yolk reserves. But at its intermediate copepod stage, the lice use their hooked antennas and frontal filaments to attach themselves to fish. At this stage they are still too small to cause any real damage as they feed on the young salmon. However, as the lice near the adult stage, they attach to the fish by suction and can become
40 | May 2018 - International Aquafeed